/*For this example, I use other schema of database*/

IF NOT EXISTS(SELECT * FROM sys.sysobjects WHERE name='Expedientes' AND xtype='U')
CREATE TABLE expedientes (
	Code			VARCHAR(15) NOT NULL,
	State			VARCHAR(20) DEFAULT 'INICIO',
	StateChangedDate	DATETIME,
	CONSTRAINT		PK_Expedientes PRIMARY KEY(code)
)

DELETE FROM Expedientes WHERE Code IN ('exp1','exp2', 'exp3');
INSERT INTO Expedientes(Code) VALUES('exp1');
INSERT INTO Expedientes(Code) VALUES('exp2');
INSERT INTO Expedientes(Code) VALUES('exp3');

/*Results*/
Code            State                StateChangedDate
--------------- -------------------- -----------------------
exp1            INICIO               NULL
exp2            INICIO               NULL
exp3            INICIO               NULL

IF NOT EXISTS (SELECT * FROM sys.sysobjects WHERE name='ExpStatusHistory' AND xtype='U')
CREATE TABLE ExpStatusHistory (
	Id		INT IDENTITY,
	Code		VARCHAR(15) NOT NULL,
	State		VARCHAR(20) NOT NULL,
	Date		DATETIME DEFAULT GETDATE(),
	CONSTRAINT	PK_ExpStatusHistory PRIMARY KEY(id)
);

/*Results*/
Id          Code            State                Date
----------- --------------- -------------------- -----------------------

IF EXISTS(SELECT 1 FROM sys.triggers WHERE name = 'StatusChangeDateTrigger')
  DROP TRIGGER StatusChangeDateTrigger
GO

CREATE TRIGGER StatusChangeDateTrigger ON Expedientes
AFTER UPDATE AS
	IF UPDATE(state)
		BEGIN
			UPDATE expedientes
			SET stateChangedDate = GETDATE()
			WHERE code = (SELECT code FROM inserted);

			INSERT INTO ExpStatusHistory(Code, State)
			SELECT Code, State
			FROM deleted
			WHERE Code = deleted.Code
		END
GO

SELECT *
FROM Expedientes

/*Results*/
Code            State                StateChangedDate
--------------- -------------------- -----------------------
exp1            INICIO               NULL
exp2            INICIO               NULL
exp3            INICIO               NULL

UPDATE Expedientes
SET State = 'PENDIENTE_COBRO'
WHERE Code = 'exp1'

SELECT *
FROM ExpStatusHistory

/*Results*/
Id          Code            State                Date
----------- --------------- -------------------- -----------------------
2           exp1            PENDIENTE_COBRO      2017-05-26 12:35:41.787

SELECT *
FROM Expedientes

/*Results*/
Code            State                StateChangedDate
--------------- -------------------- -----------------------
exp1            PENDIENTE_COBRO      2017-05-26 12:35:41.787
exp2            INICIO               NULL
exp3            INICIO               NULL